This invention relates to fasteners that have fluid embedded within their bodies such that they bleed upon failure. The detection of such fluid on the external surface of the fasteners will indicate that the fasteners have failed.
Structural members are often joined together using fasteners. When these fasteners fail due to factors such as metal fatigue or overloading, they often fracture into two or more parts such that their failure will not be visible from the outside. This is even more evident in cases where only one side of the joint is accessible and blind rivets have been used.
Prior to this invention, if the fastener is a bolt, it is always possible to test the structural soundness of the bolt by using a torque wrench. But if after installation and assembly, only one side of the bolt is accessible, such physical testing may necessitate the disassembly of the parts and physically testing the bolts one by one. Such testing can be laborious, if not prohibitively expensive.
Patents which are of background interest are:
Charles H. Popenoe, U.S. Pat. No. 3,602,186 PA1 Jack E. Mosow, U.S. Pat. No. 3,799,108 PA1 Charles E. Popenoe, U.S. Pat. No. 3,987,699
The above listed patents describe stress-strain indicators wherein a change in length of a strain member produces a change in color of a visual indicator. However, these patents are designed to measure minute displacement of the fasteners rather than their failure. When the fasteners fail, the visual indicators do show a bright color. However, the detection of fluid outside of the fasteners as described in this invention, gives a far better confirmation of fastener failure than the appearance of a bright color of the visual indicators. Moreover, the fasteners as described in this invention have the added advantage of simplicity and far lower costs due to the fact that the sole purpose of the fluid is to indicate failure of the fasteners.